In Wi-Fi communication networks, there are many known techniques for estimating the distance between a mobile device and a wireless access point. For example, the mobile device (e.g., a cell phone or tablet computer) can use the received signal strength indicator (RSSI) corresponding to the access point as a rough approximation of the distance between the mobile device and the access point, where a stronger RSSI means that the mobile device is closer to the access point and a weaker RSSI means that the mobile device is further from the access point. The mobile device can also use the round trip time (RTT) of signals transmitted to and from the access point to calculate the distance between the mobile device and the access point, where the RTT value indicates the total signal propagation time of a unicast signal sent from the mobile device to the access point and a corresponding acknowledgement signal sent from the access point back to the mobile device.
When performing distance measurements using Wi-Fi networks, issues such as hidden nodes, imbalanced interference, and/or differences in response times between various make-and-models of mobile devices can adversely affect accuracy. For example, hidden nodes in Wi-Fi networks, which can cause interference that degrades distance measurement accuracy, occurs when a node is visible from a wireless access point (AP), but not visible from other nodes communicating with the AP. Further, imbalanced interference and/or multipath effects associated with the physical surroundings of the devices (e.g., physical obstructions between and/or near the devices) can cause different components of the unicast and/or acknowledgment signals to undesirably arrive at respective devices at different times, which in turn further reduces the accuracy of distance measurements using RTT techniques.
Thus, it is desirable to improve the accuracy of distance measurements in Wi-Fi networks.
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